I'm currently hesitating between 2 Fast Attack units in order to support the core of my army (Crimson Slaughter Possessed Sorcerer, Possessed, Land Raider, Rhino, Keeper of Secrets, Daemonettes and Pink Horrors, i.e. assault and psychic powers oriented), and I would like external advises about them.

My first idea was to put a ML 2 Herald of Tzeentch into a unit of 6 Screamers, with Divination and/or Malefic Daemonology powers and an Exalted Reward (Grimoire of True Names or Portal Glyph). Such unit is really mobile, may Jink most of the time and can take care of light vehicles rather easily. But the major con is that it only has T3 due to the Herald.

Then, I have thought about a Nurgle ML 2 Sorcerer (one power in Biomancy) with a Sigil of Corruption on a bike into a unit of 4 Bikers marked by Nurgle and 2 meltaguns. No exalted reward, less jinking and mobile, but far more tough and able to deal with light and heavy vehicles.

So, which one would you include as first choice into a Chaos army list ?